# 二分查找
def binary_search(n, m):
    low = 0
    high = len(n) - 1
    while low <= high:
        mid = (low + high) // 2
        guess = n[mid]
        if guess == m:
            return mid
        elif guess < m:
            low = mid + 1
        else:
            high = mid - 1
    return -1



